(a) Field of the Invention
The present invention relates to liquid crystal displays (LCDs) and a manufacturing method thereof, in particular, to vertically-aligned liquid crystal displays (VA LCDs) having multi-domains in a pixel region and a manufacturing method thereof.
(b) Description of the Related Art
A liquid crystal display (LCD) includes two substrates and a liquid crystal layer interposed therebetween. The transmittance of the incident light is controlled by the strength of the electric field applied to the liquid crystal layer.
A vertically aligned twisted nematic (VATN) liquid crystal display has a couple of transparent substrates which have transparent electrodes respectively on their inner surfaces, a chiral nematic liquid crystal layer having negative anisotropy between the substrates and a couple of polarizers which are respectively attached to the outer surfaces of the substrates. In the off state of the LCD, i.e., in the state that the electric field is not applied to the liquid crystal layer, the molecular axes or the long axes of the liquid crystal molecules are perpendicular to the substrates. On the other hand, in the on state of the LCD, i.e., in the state that the sufficient electric field caused by the voltage different between the electrodes is applied to the liquid crystal layer, the long axes of the liquid crystal molecules are parallel to the substrates by the negative anisotropy and twisted spirally by the chirality with a pitch from the inner surface of one substrate to the other substrate. Accordingly, the orientation of the long axes of the liquid crystal molecules vary continuously.
A VATN LCD in normally block mode may have an off state which is sufficiently dark because the molecular axes of the liquid crystal molecules are uniformly aligned perpendicular to the substrates in the off state. Therefore, the contrast ratio is relatively high compared with a conventional TN LCD. In addition, the viewing angle may be strongly dependent on the viewing directions. Therefore, it is suggested to form multi-domains in a pixel by providing apertures in the electrode by Clere in U.S. Pat. No. 5,136,407 and by Hirose in U.S. Pat. No. 5,229,873, etc.
One object of the present invention is to form patterns for multi-domains to enlarge to range of viewing angle.
Another object of the present invention is to reduce the steps of forming patterns for multi-domains.
Another object of the present invention is to reduce light leakage near the boundary of multi-domains to improve the contrast ratio.
To achieve these objects of the present invention, aperture pattern is formed in pixel electrodes on a TFT substrate and protrusion pattern is formed on a color filter substrate to form multi-domain alignment of liquid crystal.
A liquid crystal layer having negative dielectric anisotropy may be interposed between the substrates, and alignment layers may be formed on inner surfaces of the substrates respectively.
A pair of polarizers of which the polarzing directions are preferably perpendicular to each other may be attached to outer surfaces of the substrates.
Compensation films may be attached between one of the substrates and one of the polarizers attached thereto, and a biaxial or a combination of an a-plate and a c-plate compensation films may be used. The slow axis of the biaxial or the a-plate compensation film is preferably parallel or perpendicular to the polarizing directions of the polarizers.
The aperture pattern and the protrusion pattern may be formed as a shape of a wedge at an angle of 45 degrees with respect to the polarzing axis of the polarizers.
The aperture pattern may be cross-shaped or X-shaped perpendicular to the polarizing axis of the polarizer and the protrusion pattern may be tetragon shape surrounding the aperture pattern. The width of the cross-shaped pattern decreases as goes from a center to the edge of the pattern.
The width of the aperture pattern, the width of the protrusion pattern and the height of the protrusion pattern are 3 to 20 microns, 3 to 20 microns and 0.3 to 3 microns respectively.
Black matrix overlapping the protrusion pattern may be formed on the upper substrate and a wire overlapping the aperture pattern may be formed on the lower substrate.
To achieve the objects of the present invention, a pixel electrode having wedge-shaped aperture pattern is formed on the lower substrate and protrusion pattern arranged to the aperture pattern alternately and in parallel are formed on the upper substrate.
In the upper substrate, a black matrix overlapping the aperture pattern may be formed.
The black matrix may include the fist portion overlapping the protrusion pattern, the second portion put across the bent points of the wedge-shaped aperture pattern and the protrusion pattern and the third portion covering a portion that the aperture pattern and the protrusion pattern meet a boundary of the pixel electrode.
The third portion of the black matrix may be formed as a triangular shape.
The black matrix may include the fourth portion overlapping the aperture pattern.
The edge of the pixel electrode between the aperture pattern and the protrusion pattern may be perpendicular to the aperture pattern.
In a manufacturing method of the present invention, aperture patterns of the TFT substrate are simultaneously formed at the step of forming the pixel electrode. Then protrusion pattern is formed on the color filter substrate in a manner to arrange to the aperture patterns alternately and in parallel.
The protrusion pattern may be formed by coating a photo-sensitive film, exposing, developing and baking the film.
As described, the aperture pattern is formed at the step of patterning the ITO pixel electrode and a passivation film may not be coated on color filters. As a result, the number of the manufacturing steps decrease.